3
TABLE 2. RESOLUTION CONTROL (A AND B)
RESOLUTION
B
A
10 bit
0
12 bit
0
1
14 bit
1
0
16 bit
1
THEORY OF OPERATION
The SD-14620 Series of converters are based upon a single chip
CMOS custom monolithic. Using the latest technology, precision
analog circuitry is merged with digital logic to form a complete,
high-performance tracking synchro/resolver-to-digital (S/D, R/D)
converter.
CONVERTER OPERATION
FIGURE 1 is the Functional Block Diagram of the SD-14620
Series. The converter operates with a single +5 VDC power sup-
ply and each channel internally generates a negative voltage of
approximately 5 volts. These negative voltages are connected to
pin 52 (channel “A” filter point) and pin 24 (channel “B” filter
point) — see GENERAL SETUP CONSIDERATIONS.
The converter is made up of three main sections; an input front-
end, an error processor, and a digital interface. The converter
front-end differs for synchro, resolver and direct inputs. An elec-
tronic Scott-T is used for synchro inputs, a resolver conditioner
for resolver inputs, and a sine and cosine voltage follower for
direct inputs. These amplifiers feed the high accuracy Control
Transformer (CT). Its other input is the 16-bit digital angle
φ. Its
output is an analog error angle, or difference angle, between the
two inputs. The CT performs the ratiometric trigonometric com-
putation of SIN
θCOSφ - COSθSINφ = SIN(θ - φ) using amplifiers,
switches, logic, and capacitors in precision ratios. The converter
accuracy is limited by the precision of the computing elements in
the CT. Ratioed capacitors are used in the CT in these convert-
ers, instead of the more conventional precision ratioed resistors.
Capacitors that are used as computing elements with op-amps
are sampled at a high rate to eliminate drift and the op-amp off-
sets.
The error processing is performed using the industry standard
technique for type II tracking R/D converters. The DC error is
integrated yielding a velocity voltage which in turn drives a volt-
age- controlled oscillator (VCO). This VCO is an incremental inte-
grator (constant-voltage input to position-rate output) that,
together with the velocity integrator, forms a type II servo feed-
back loop. A lead in the frequency response is introduced to sta-
bilize the loop and a lag at a higher frequency is introduced to
reduce the gain and ripple at the carrier frequency and above.
GENERAL SET-UP CONSIDERATIONS
The following recommendations should be considered when
connecting the SD-14620 Series converters:
1) The +5 VDC power supply input is on pin 18. For performance
with the lowest amount of noise it is recommended that a
10 F/10 VDC (or larger) tantalum filter capacitor be connect-
ed to ground (pin 19) near the converter package.
2) Direct inputs are referenced to Analog Ground (A GND).
Connections should made as close to the converter package
as possible to minimize noise. Channel A should be refer-
enced to A GND-A (pin 5) and Channel B should be refer-
enced to A GND-B (pin 32).
3) A 47 F/10 V tantalum filter capacitor must be added exter-
nally from pin 52 (channel “A” filter point) to pin 19 (ground). In
addition, a 47 F/10 Vdc tantalum filter capacitor must be
added externally from pin 24 (channel “B” filter point) to pin 19
(ground).
SPECIAL FUNCTIONS
PROGRAMMABLE RESOLUTION
Resolution is controlled by pins 49 and 50 for channel A; pins 21
and 22 for channel B. The resolution can be changed during con-
verter operation, so the appropriate resolution and velocity
dynamics can be changed as needed. To insure that a race con-
dition does not exist between counting and changing the resolu-
tion, the resolution control is latched internally. Refer to TABLE 2
for Channel A and B resolution control.
BIT, (BUILT-IN-TEST)
This output is an active low logic line that will flag an internal fault
condition or LOS (Loss-Of-Signal). The internal fault detector
Note: HBE enables the MSB byte and LBE enables the LSB byte.
10800
5400
2700
1350
675
337.5
168.75
84.38
42.19
21.09
10.55
5.27
2.64
1.32
0.66
0.33
180
90
45
22.5
11.25
5.625
2.813
1.406
0.7031
0.3516
0.1758
0.0879
0.0439
0.0220
0.0110
0.0055
1 (MSB ALL MODES)
2
3
4
5
6
7
8
9
10 (LSB 10-BIT MODE)
11
12 (LSB 12-BIT MODE)
13
14 (LSB 14-BIT MODE)
15
16 (LSB 16-BIT MODE)
MIN/BIT
DEG/BIT
BIT
TABLE 3. DIGITAL ANGLE OUTPUTS